Although several rivers flow through the area Jia-Li, Xue-Jia and Yan-Shui Town in the Tainan County, the water supply from the rivers in the dry season is quite different from that in the raining season. In addition the three towns are located in the downstream region of the rivers, the water quality is therefore not good. Furthermore for a lack of water dam or other reservoirs, which keep excess water in reserve during the raining season, the most residents in these towns can only depend on the water supply from the upriver water reservoir or pump ground water. However the clay stratification restricts the supplemental effects of ground water to the water supply for the people. Nowadays the overdrawing of ground water results in the descent of the water table below sea level, seawater intrusion, subsidence of this area and ground water pollution and so on.
